Radiometric measuring of thin fluid films

ABSTRACT

Methods and devices relate to radiometric measurement of a thin fluid film ( 4 ) using absorption of IR radiation. At least one IR radiator ( 1 ) is directed to send signals to an IR detector ( 2 ) via a bed ( 3 ) on which the fluid film ( 4 ) is placed. The IR detector is set to receive IR radiation in a band around a characteristic absorption band of the fluid of the fluid film ( 4 ). The present invention is developed for printing presses, where the thickness of fountain solution on the printing plate and the proportion of printing ink in an emulsion of printing ink and fountain solution may be controlled.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 10/443,026 filed May 22, 2003, which is acontinuation application of International Application No. PCT/SE01/02592filed Nov. 23, 2001, and which was published in English, the entirecontent of both of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention concerns radiometric measurement of thin fluidfilms, using absorption of IR radiation.

2. Description of Related Art

It is known that different substrates absorb different, specific bandsof IR (infrared) radiation. Thus, by directing IR radiation towards athin film of the substrate it is possible to determine the thickness ofthe film. By a radiometric analysis it is further possible to determinethe proportion of ingredients in the substrate and by continuousmonitoring it is possible to establish changes of said proportion.Radiometric analysis is based on the change of energy or absorption ofradiation, which in this case has wavelengths within the IR area.

The invention is developed for a printing press but may be used formeasurement and control of any thin fluid film. Other applicationsinclude but are not limited to: oil films often used in pressing ofsheet metal; coatings on paper or metal; and photographic films onsubstrates within the semiconductor industry.

In a printing press, especially but not exclusively an offset printingpress, printing ink is to be supplied to the printing areas of theprinting plates, whereas all other areas of the printing plates are tobe covered by fountain solution during the entire printing process. Thefountain solution is normally a water-based solution. Due to differentsurface conditions on the printing plates the printing ink and thefountain solution will only adhere to the intended areas. Thus, theprinting plates have printing areas and non-printing areas. In theprinting areas there will be a thin film of an emulsion of fountainsolution and printing ink. In the non-printing areas there will be athin film of fountain solution, which also may include a small portionof ink pigments.

The supply of printing ink is performed by means of inking units (oneunit per colour), whereas fountain solution is normally supplied bymeans of a spray bar or other equivalent device, with a lengthcorresponding to the width of the printing press or the length of theprinting cylinder. The spray bar usually contains spray nozzles, butother supply means are also possible. From the spray bar the fountainsolution is normally transferred to the printing plates by means of oneor more form rollers.

The provided amount of fountain solution and printing ink is normallyset to values predetermined for the actual printing situation. However,it is also controlled by the printer, who by an experienced eyesupervises the printing plates and sees to it that proper amounts aresupplied. However, this manual control lacks proper accuracy and cannotcope with rapid changes in the conditions. Accordingly, the printingresult will not be optimal, even if the printer is extremelyexperienced. It is also common to have a density meter for control ofthe printing quality.

SUMMARY

The method and device of the invention is based on absorption ofradiation having wavelengths within the IR area, using the main or otherabsorption bands of a fluid to be measured and using the change ofenergy when the radiation passes through a thin fluid film.

A further important condition is that the object on which the fluid filmis received reflects a major part of the radiation in the selectedwavelength range.

One object of the present invention is to be able to continuouslymonitor the thickness of a thin fluid film. The measurements arepresented in real time or after being processed.

Another object of the present invention is to monitor the proportion ofingredients in the fluid film in real time or after subsequentprocessing of the received measurement signals.

A further object of the present invention is to optimise the printingresult of printing presses. This is done by optimising both the amountsof fountain solution and the proportion between printing ink andfountain solution in the emulsion in order to obtain the desired densityin the printed area on the paper.

The above objects are achieved with a method and a device according tothe present invention. The method is radiometric measurement of thinfluid films using absorption of IR radiation. At least one IR radiatoris directed to send signals to a connected IR detector by means of thefluid film to be measured. The method is used for a printing press.Thus, the fluid film consists of fountain solution or an emulsion offountain solution and printing ink, received on a printing plate orother printing equipment. The measurement device is formed of at leastone unit comprising the IR radiator and the IR detector, a signalprocessing system and other support systems. The at least one unitmeasures on a non-printing area and/or a printing area of the printingplate. A control unit is arranged to receive information from furthersensors and meters.

By using radiometric measuring it is possible to measure accurately evenon very thin films, as the radiometric measuring will give strongsignals. If the radiation signals are sent more or less in parallel theaccuracy will improve further.

For printing presses the amount of fountain solution and printing ink onthe printing plates is monitored and optimised by the invention, whichreduce the waste of fountain solution and printing ink. As the printingis optimised and constantly controlled regarding fountain solution andprinting ink there will be less waste of paper and printing ink. Lesswaste of paper and printing ink leads to less negative environmentalinfluence.

One problem that may occur during printing is toning, which is wellknown in the art of printing. As used in this description the expression“toning” stands for that the contrast between the printed andnon-printed areas deteriorates. Toning may occur if excessive amount offountain solution is received in printing areas. It may also occur ifink is received in non-printing areas. Toning is often due to the factthat either too much or too little fountain solution is delivered. Ifink is deposited in non-printing areas it is normally referred to asscumming. Water deposited in the printing areas leads to so-calledwatermarks and failure of printing areas to accept ink leads toso-called blinding. Thus, it is an object of the present invention to beable to warn against any of the above problems and to correct the supplyof fountain solution and possibly the supply of ink before any suchproblems occur.

Further objects and advantages with the present invention will beobvious for a person skilled in the art when reading the descriptionbelow of example, non-limiting embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Example, non-limiting embodiments of the invention will become fullyunderstood from the detailed description below and the accompanyingdrawings, wherein like elements are represented by like referencenumerals, which are given by way of illustration only and thus are notlimiting of the present invention.

FIG. 1 is a principal illustration of the method according to anexample, non-limiting embodiment of the present invention.

FIG. 2 is a block diagram showing the method according to an example,non-limiting embodiment of the invention used at a printing press.

FIG. 3 is a diagram showing an example, non-limiting embodiment of howan IR range for measurement may be determined.

FIG. 4 is a cross section view of an example, non-limiting embodiment ofa unit comprising IR radiator and IR detector.

DESCRIPTION OF EXAMPLE, NON-LIMITING EMBODIMENTS

The expression “fluid film” is used in the present description both fora fountain solution (often water-based) and an emulsion of printing inkand fountain solution in connection with printing presses. The fountainsolution is received on the non-printing areas of the printing plate orprinting surface. The fountain solution is normally an emulsion of waterand a few percentages of additives. The fountain solution may alsoinclude a small portion of ink pigments when it is received on theprinting plate. The emulsion of printing ink and fountain solution isreceived on the printing areas of the printing plate or surface.

In FIG. 1 the principle for the present invention is shownschematically. A thin fluid film 4 is received on a bed 3. For printingpresses the bed 3 is a printing plate or other printing equipment. An IRradiator 1 directs IR radiation towards the thin fluid film 4 and an IRreceiver or detector 2 receives the IR radiation after passage of thethin fluid film 4. Thus, the bed 3 must reflect a major part of the IRlight sent by the radiator 1.

The IR detector 2 normally functions best if the IR light is pulsated.To accomplish this, a mechanical device (not shown) may be placed at theradiator 1 or detector 2, which device intermittently blocks the IRradiation. A further example is that the IR radiator 1 is driven in anelectrical pulse mode. As devices for pulsating are commonly known topersons skilled in the art they will not be described further here. Thepresent invention may also be used with a continuous IR light.

The IR radiator 1 and IR detector 2 are normally connected to a signalprocessing unit (not shown) and other support systems (not shown). Bymeans of the signal processing system the absorbed energy of the thinfluid film 4 is calculated. The thickness of the fluid film 4 ismonitored continuously.

Furthermore, if the radiator 1 is directed to a printing area theproportion of printing ink in the fluid film 4 may be determined.

FIG. 2 shows an example of a system according to the invention used at aprinting press. This embodiment comprises two sensor units 5, 6, eachhaving an IR radiator and an IR detector. In this case the IR light maybe sent more or less in parallel. In the shown example one of the sensorunits 5 is directed to a non-printing area 12 of the printing plate andthe other sensor unit 6 is directed to a printing area 13 of theprinting plate 3. In the non-printing area 12 the thickness of thefountain solution is measured. In the printing areas the fluid film 4consists of an emulsion of fountain solution and printing ink and theproportion of printing ink in the emulsion is deter-mined. To calculatethe proportion of printing ink in the emulsion the thickness of thefountain solution, as measured by the sensor unit 5 is employed.

In FIG. 4 one example of a set-up to give parallel IR radiation beams isshown. Inside a housing 15 an IR radiator 16 is placed. The IR radiator16 radiates into a radiation tube 17. By means of the radiation tube 17the radiation beams will be parallel when leaving the radiation tube 17.Non-parallel radiation beams are extinguished in that they will notreflect from the inner surface of the radiation tube 17. The innersurface of the radiation tube 17 is made or treated to benon-reflective. From the radiation tube 17 the radiation is led to afluid film on a surface. The radiation is reflected from the surface ina scattered way and is directed by means of a reflector 18 towards oneor more detectors 19.

The signals from the detector of each sensor unit 5, 6 are forward to acontrol unit 7. Normally the control unit 7 communicates with anexisting control unit 14 of the printing press. Signals from an anglesensor 8 and a density meter 9 are also transferred to the control unit7. The angle sensor 8 is used to establish the position of the printingplate 3 and, thus, the point to be measured. The density meter 9 is usedfor measurement on the printed paper and gives an indication of theprinting quality. The control unit 7 sends signals to a controller 10for fountain solution and a controller 11 for printing ink. Based on theinformation forwarded to the control unit 7, it will send signals to thecontroller 10 for fountain solution and/or the controller 11 forprinting ink to increase or decrease the supply of fountain solution andprinting ink, respectively, if necessary.

By means of the angle sensor 8 the rotational position of a printingplate may be established. A sensor unit comprising at least one IRradiator and one IR detector may be moved in axial direction in relationto the printing plate. By such an axial movement of the sensor unit andby controlling the rotational position of the printing plate by means ofthe angle sensor 8, any optional point of measuring can be reached onthe printing plate.

Before starting the actual measurements the sensors are calibrated on anempty printing plate, to adjust the force of the signal. The minimalforce to be used is normally the force, which gives a full signal withan empty printing plate.

To start the measurement according to the invention one or morecharacteristic absorption band for the fluid film 4 is normally firstdetermined. For printing presses the fluid of the fluid film 4 is eithera fountain solution or an emulsion of fountain solution and printingink. The absorption band is to be in the IR range. The determination ofthe one or more characteristic absorption band is normally done by aspectral analysis of the fluid of the fluid film 4. Preferably the mainabsorption band of the fluid film 4 is used. However, a person skilledin the art realizes that also other absorption bands of the fluid may beused. Which other absorption bands may reflect separate ingredients ofthe fluid. Based on this information the IR detector 2 is set to receiveradiation in a band around the chosen characteristic absorption band.The band is normally given by means of one or more filters placed on theIR detector 2. The one or more filters may also be placed at the IRradiator 1. The IR radiator 1 is often set to send IR light in a broadrange. When the IR light is sent in a broad range the radiator 1normally does not have to be adjusted, any adjustment is done bychanging the filter at the detector 2 or radiator 1. It is also possibleto use an IR radiator sending IR light in a narrow range, which narrowrange is adapted to the chosen characteristic absorption band.

Instead of using filters to give one narrow band it is possible to usean IR spectrometer (not shown). As is well known an IR spectrometer willgive the spectral characteristic of the received IR light. In thisrespect it could be said that the IR detector 2 forms a part of the IRspectrometer.

In FIG. 3 a method to determine the band in which IR radiation is to bereceived by the IR detector 2 is indicated. To decide a proper IR bandthe actual absorption band from the spectral analysis is used. The aimwith the method of FIG. 3 is to arrive at a narrow band corresponding toa major part of the actual absorption band. Thus, the absorptionfarthest out on both sides of the actual absorption band may bediscarded. Depending on the form of the actual absorption band a value Cbeing a major fraction of the maximal value in y-direction is chosen.Then the positions A, B on the x-axle related to the value C aredetermined. The band between the positions A and B is then used as theband in which IR radiation is to be received by the IR detector 2. Aperson skilled in the art realizes that other methods may be used todetermine a suitable band of IR light to be received by the detector 2.

When an appropriate absorption band has been determined, the IR radiator1 and IR detector 2 and/or sensor units 5, 6 are set to measure one ormore points in real time. It is also possible to process the signalsbefore the values are presented. It is also possible to use only one ofthe sensor units 5, 6 to measure on printing and non-printing areas 12,13, whereby the angle sensor 8 is used to establish the printing areaand non-printing area, respectively.

If two or more points are to be monitored simultaneously two or moresensor units 5, 6, containing an IR radiator 1 and an IR detector 2 areused. When two or more points are monitored, by two or more sensor units5, 6, one point is normally a non-printing area 12 and the other pointis a printing area 13.

If the two or more points do not have to be monitored simultaneously,one single unit may be used. The single unit will be moved between thepoints to be monitored so as to measure at each point one at the time inrapid succession. As indicated above the angle sensor 8 is used toestablish the rotational positions of the points to be measured. Theband of received IR radiation may be altered for each point. Thus, thesame unit may be used for measuring alternately at printing areas andnon-printing areas.

The measurements are used to constantly control the delivery of fountainsolution and printing ink.

It is also possible to show the measurement of the detector 2 or sensorunit 5, 6 locally, i.e. without sending any signals to any control unit7 of the printing press. In this case the printer may decrease orincrease the amount of fountain solution and/or printing ink feed to theprinting plate based on the shown measurement values.

What is claimed is:
 1. A method for radiometric measurement of thinfluid films where absorption of IR radiation is used, the methodcomprising: directing at least one IR radiator to send signals to aconnected IR detector by means of the fluid film to be measured, whereinthe method is used for a printing press, and the fluid film comprisesfountain solution or an emulsion of fountain solution and printing ink,received on a printing plate; constantly monitoring the fluid film; andpulsating the signals; wherein one or more filters are placed at the IRdetector to limit the received IR radiation to a band and wherein thesignals from the IR radiator to the IR detector are sent in parallel. 2.The method of claim 1, wherein one or more points to be measured isestablished by positioning a sensor unit comprising at least one IRradiator and one IR detector in a predetermined position in axialdirection of the printing plate and using an angle sensor to determinethe rotational position on the printing plate.
 3. The method of claim 2,wherein the sensor unit is moved axially in view of different points tobe measured on the printing plate.
 4. The method of claim 2, wherein thepoints to be measured are chosen either as a printing area or anon-printing area of the printing plate.
 5. The method according toclaim 1, wherein the IR radiation beams are made passing a radiationtube before reaching the fluid film to be measured, whereby non-parallelradiation beams are extinguished by not reflecting from the insidesurface of the radiation tube.
 6. The method according to claim 1,wherein the printing press is an offset press.
 7. The method accordingto claim 1, wherein the proportion of ingredients of the emulsion offountain solution and printing ink is measured and the measurement isrelated to measurement of the thickness of the fluid film, the supply offountain solution and/or printing ink is adjusted in view of themeasurements
 8. The method according to claim 2, wherein the signalsfrom the at least one IR detector are given to a control unit, thesignals of the angle sensor and a density meter are given to the controlunit and the signals from related detectors, sensors and meters areprocessed in the control unit to control the supply of fountain solutionand/or printing ink.
 9. The method according to claim 8, wherein themeasurements are presented in real time or after processing of themeasurements, the IR radiator sends IR radiation in a broad or narrowrange, one or more filters are placed at the IR detector or IR radiatorto limit the received IR radiation to a band and that the absorptionband is the main absorption band of the fluid to be measured.
 10. Themethod according to claim 1, wherein an IR spectrometer is used.
 11. Themethod according to claim 1, wherein several points of measurement aremonitored and that the power of IR radiation in at least one of thepoints of measurement is set in relation to a specific printing ink. 12.The method according to claim 1, wherein a characteristic absorptionband of the fluid of the fluid film is first determined, wherein thewavelength of the IR radiation to be received by the IR detector is setto a band in a range where the fluid or separate ingredients of thefluid has significant absorption and wherein the characteristicabsorption band is determined by means of spectral analysis and the IRrange set to be received by the IR detector corresponds to a major partof the chosen characteristic absorption band of the fluid.
 13. A devicefor radiometric measurement of thin fluid films where absorption of IRradiation is used, comprising: at least one unit comprising an IRradiator and an IR detector, which are placed to send and receivesignals sent in parallel; a signal processing system and other supportsystems provided at a printing press, wherein the at least one unitmeasures on a non-printing area and a printing area of the printingplate; and a control unit for receiving information from further sensorsor meters.
 14. The device according to claim 13, wherein a radiationtube is placed between the IR radiator and the film to be measured,which radiation tube has a non-reflective inner surface.
 15. The deviceaccording to claim 13, wherein the at least one unit is moveable inaxial direction in relation to the printing plate.
 16. The deviceaccording to claim 13, wherein the at least one unit is fixed.
 17. Thedevice according to claim 13, wherein the at least one unit comprises anIR spectrometer.
 18. The device according to claim 13, wherein themeasurements are presented locally.
 19. The device according to claim13, wherein a separate unit is used for each point of measurement. 20.The device according to claim 13, wherein controllers for delivery offountain solution and printing ink are connected to the control unit.